1. Field of the Invention
This invention broadly relates to a composition useful for imparting fire resistance to a variety of substrates, such as materials used in the building and construction industry. More particularly, this invention provides an aqueous composition containing as essential components an acid-hardenable melamine-formaldehyde resin W resin) and an acidic curing agent selected from a particular class of nitrogen-containing acidic phosphorus compounds made from either phosphoric acid or phosphorous acid. After curing, this composition acts as an intumescent and imparts fire resistance to substrates treated with the composition.
2. Description of Related Art
Intumescent coatings are commonly applied to the surface of construction materials. Such coatings serve, for example, to prevent the spread of fire. Intumescent coatings are also applied to the surface of other flammable substrates, to reduce their flammability. U.S. Pat. No. 4,198,328 for example, describes an intumescent paint which includes a source of phosphoric acid, a carbon source and an expanding agent. These components are bound together by a conventional polymeric binder. Binders have included acrylic styrene or vinyl toluene copolymer, a styrene or vinyl toluene-butadiene-copolymer, a styrene or vinyltoluene-acrylonitrile-copolymer polyurethane resins, alkyl resins and the like. Alternatively, polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, urea or melamine-formaldehyde resins and vinyl chloride-vinylidene chloride copolymers have been used. The use of epoxy resins in combination with various amino-functional curing agents also is known. In all of these formulations chlorinated paraffins or optionally chlorinated phosphate esters may be employed as plasticizers.
Other intumescent systems are also known. GB-A-2,151,237 discloses water-insoluble formulations which contain chlorinated polymers, novolak resin and chlorinated or phosphorylated plasticizers. GB-A-2,012,296 describes a three-layer intumescent paint which uses as the intermediate layer formulations which contain expandable graphite, hydrated alumina and binder systems based on halogenated elastomers and alkyl phenol-formaldehyde resins. The binder, in concert with a silicate top coating, functions to prevent the expanded graphite from crumbling and cracking. GB-A-1,604,908 mentions products with vermiculite and inorganic fibers as filler as well as elastomeric binders and clay.
Intumescent, fire resistant compositions act by forming an expanded, insulating layer of a hardly flammable material under the action of heat. The expanded layer shields the substrate from oxygen and/or from overheating and thereby prevents or delays the spread of flame, and prevents or at least delays reductions in the mechanical and static properties of structural supporting elements caused by heat.
A greater expansion (intumescence) produces thicker protective layers, but at the same time the thicker layers, generally due to their reduced mechanical stability, often are more easily detached from the substrate thus becoming less effective.
Conventional intumescent systems consist of a binder of the above type including urea-formaldehyde resins and melamine-formaldehyde resins, a char or carbon skeleton forming substance (typically referred to as "carbonific"), an expanding agent (typically referred to as "spumific") and an acid forming substance as essential components. As carbonifics, organic polyhydroxy compounds such as pentaerythritol, dipentaerythritol, tripentaerythritol, starch and sugars have been employed. Examples of spumifics are nitrogen-containing compounds such as melamine, melamine salts, melamine derivatives, urea, dicyandiamide and guanidine. The spumific effects the formation of a foamed (intumescent) layer by emission of an inert gas. As acid forming substances usually an aminophosphate, mainly ammonium phosphates and amine phosphates, preferably ammonium polyphosphate, and melamine phosphate, have found use. Examples of further additives are inorganic fibers which are to increase the mechanical strength of the intumescent layer and/or to prevent the dripping thereof, and metal oxides which act as smoke suppressants. Typical examples of such compositions can be found in U.S. Pat. Nos. 4,442,157, 4,638,538, 3,562,197, and GB-A-755,551.
Upon exposure to a flame, an intumescent composition swells up with the formation of a foam which repels the action of the fire. Many intumescence compositions, used, for example, as fire-preventive coatings or fire-preventive cements, on exposure to a flame form carbonization foams, because they contain, as intumescence media, carbohydrates or phenolic, polyurethane or melamine resins in combination with a phosphoric acid donor. Inorganic materials, for example alkali metal silicates containing water, can also foam up on exposure to a flame, and also are employed for the purposes of fire prevention. However, since these silicates are sensitive to air, moisture and/or CO.sub.2, they can only be used to a limited extent as intumescence media.
In most organic-compound based intumescence compositions, carbonisable compounds in combination with phosphorus compounds act as the intumescence media. The carbonization foams formed on exposure to a flame have, however, only a low mechanical strength, put up only a low resistance to flame erosion and are degradable by oxidation. Organic fire-preventive materials of this type can also contain aluminum hydroxide, the function of which is to assist the foaming up of the carbonization melt by splitting off water under the influence of heat, and to carry off heat.
The carbonization of organic melts is promoted by phosphorus compounds which liberate phosphoric acid. As noted above, ammonium phosphates are therefore frequently employed as phosphoric acid donors, but their good solubility in water has often been considered a disadvantage.
There is, therefore, still a need for intumescence compositions which are not degradable by oxidation, which are insensitive towards air, moisture and CO.sub.2, which upon exposure to a flame become effective and form as far as possible an intumescent foam having mechanical stability.
Accordingly it is an object of the present invention to provide a composition having integrated intumescent properties which avoids or at least alleviates disadvantages of conventional prior art intumescent systems described above.
Compliance with various fire resistance testing methods is an important consideration in developing fire resistant compositions because many regulatory agencies and building codes rely on these tests in determining the acceptance of building materials used in various applications. Insurance rates may also be affected by compliance with fire resistance testing methods. In the present invention, fire resistance of the composition was determined in part using the Cone Calorimetric Test (ASIM E1354), the Tunnel Test (ASTM E-84), the Heat Release Test (ASTM E-906 and the Smoke Test (ASTM E-662).